scholarly journals Slow and sausage loop mode excitation due to local and global spontaneous perturbations

2020 ◽  
Vol 644 ◽  
pp. A106
Author(s):  
H. Capettini ◽  
M. Cécere ◽  
A. Costa ◽  
G. Krause ◽  
O. Reula

Aims. We analyse the capability of different types of perturbations associated with usual environment energy fluctuations of the solar corona to excite slow and sausage modes in solar flaring loops. Methods. We performed numerical simulations of magnetohydrodynamic ideal equations with a consideration of straight plasma magnetic tubes subject to local and global energy depositions. Results. We find that local loop energy depositions of typical microflares [∼(1027 − 1030) erg] are prone to driving slow shock waves that induce slow-mode patterns. The slow-mode features are obtained for every tested local energy deposition inside the loop. Meanwhile, in order to obtain an observable sausage mode pattern, a global perturbation that is capable of instantaneously modifying the internal loop temperature is required; specifically, the characteristic conductive heating time must be much smaller than the radiative cooling one. Experiments carried out by varying the parameter β demonstrate that the excitation of sausage modes does not significantly depend on the value of this parameter but, rather, depends on the global or local character of the energy source.

2014 ◽  
Vol 1040 ◽  
pp. 965-968 ◽  
Author(s):  
Yuliana K. Atroshenko ◽  
Irina P. Ozerova ◽  
Pavel A. Strizhak

In the present article the question of simulation of nonstationary process of heat transport in a sensitive element of the thermoelectric transformer with an uninsulated seal is considered. The model allows defining and comparing the heating time of a thermocouple junction up to the given temperature for different types of thermocouples. In this article the values obtained by means of modelling the heat time of different thermocouples and also a temperature field in a sensitive element of the thermoelectric transformer are given.


2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Janmejay Dattatraya Kulkarni ◽  
Suresh Babu Goka ◽  
Pradeep Kumar Parchuri ◽  
Hajime Yamamoto ◽  
Kazuhiro Ito ◽  
...  

Purpose The use of a gas metal arc welding-based weld-deposition, referred to as wire-direct energy deposition or wire-arc additive manufacturing, is one of the notable additive manufacturing methods for producing metallic components at high deposition rates. In this method, the near-net shape is manufactured through layer-by-layer weld-deposition on a substrate. However, as a result of this sequential weld-deposition, different layers are subjected to different types of thermal cycles and partial re-melting. The resulting microstructural evolution of the material may not be uniform. Hence, the purpose of this study is to assess microstructure variation along with the lamination direction (or build direction). Design/methodology/approach The study was carried out for two different boundary conditions, namely, isolated condition and cooled condition. The microstructural evolution across the layers is hypothesized based on experimental assessment; this included microhardness, scanning electron microscopy imaging and electron backscatter diffraction analysis. These conditions subsequently collaborated with the help of thermal modeling of the process. Findings During a new layer deposition, the previous layer also is subject to re-melt. While the newly added layer undergoes rapid cooling through a combination of convection, conduction and radiation losses, the penultimate layer, sees a slower cooling curve due to its smaller exposure area. This behavior of rapid-solidification and subsequent re-melting and re-solidification is a progressing phenomenon across the layers and the bulk of the layers have uniform grains due to this remelt-re-solidification phenomenon. Research limitations/implications This paper studies the microstructure variation along with the build direction for thin-walled components fabricated through weld-deposition. This study would be helpful in addressing the issue of anisotropy resulting from the distinctive thermal history of each layer in the overall theme of metal additive manufacturing. Originality/value The unique aspect of this paper is the postulation of a generic hypothesis, based on experimental findings and supported by thermal modeling of the process, for remelt-re-solidification phenomenon followed by temperature raising/lowering repetitively in every layer deposition across the layers. This is implemented for different types of base plate conditions, revealing the role of boundary conditions on the microstructure evolution.


1988 ◽  
Vol 8 (2-4) ◽  
pp. 123-135 ◽  
Author(s):  
A. V. Dem'Yanenko ◽  
G. A. Polyakov ◽  
A. A. Puretzky

We studied the IR luminescence spectra of vibrationally excited CF2Cl2 molecules resulting from excitation of the ν1 (1098 cm−1) and ν8 (922 cm−1) modes with a pulsed CO2 laser. The nonequilibrium spectra obtained under pumping conditions where their equilibrium counterparts coincide (the number of the photons absorbed per molecule being the same) were found to differ considerably. We suppose that this difference is due to different types of vibrational distribution formed as a result of the IR laser pumping. When pumping the ν1 mode, excitation of the R-branch occurs, resulting in the molecules “sticking” on the lower vibrational levels, whereas in the case of the ν8 mode, it is the P-branch that gets excited so that the molecules become easy to raise to high-lying vibrational levels.


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